ABSTRACT
The rich global biodiversity is threatened with erosion on an unprecedented scale. While the rates of extinction were roughly equal to those of speciation for most of the history of life on earth, contemporary extinction rates are several times faster than those of speciation leading to erosion of Biodiversity (UNEP, 1995). Wemay already be losing 50 to 100 species per day (Myers, 1986). Conservation biologists caution that 25 percent of all species could become extinct during the next 20 to 30 years. During the last 200 million years about 100 species became extinct in each century due to natural evolutionary processes. At the same time evolution ushered in new life forms that more than compensated the species lost. Today the extinction rate is approximately 40,000 times higher than this background rate due to the depredations of Homo sapiens. The Holocene extinction rates of decline in biodiversity in this sixth mass extinction match or exceed rates of loss in the five previous mass extinction events in the fossil record. Previous mass extinctions had no palpable effect on terrestrial plants; but today for the first time an enormous proportion of terrestrial plant species which form the basis of land ecosystems are threatened (Knoll, 1984). A disappearing plant can take with it 10 to 30 dependent species such as insects, higher animals and even other plants. In 2006 many species were formally classified as rare or endangered or threatened. Moreover, scientists have estimated that several species are at risk which have not been formally recognized. About 40 percent of the 40,177 species assessed using the IUCN Red List criteria are now listed as threatened with extinction. There is a growing concern on the prospect of accelerating loss of species, populations, domesticated varieties and natural habitats such as tropical rainforests and wetlands. Recent estimates suggest that more than half the habitable surface of the planet has been significantly altered by human activity. World Conservation and Monitoring Centre (WCMC, 1992) has estimated the number of species of plants and animals extinct since 1600 as 654 and 484 respectively. One of the estimates suggests that tropical forests are being denuded
at the rate of 15.4million ha per annum or approximately 1.8% of the remaining forest cover. This will undoubtedly cause the loss of innumerable species and populations of plants and animals and thus will impoverish the global species and genetic diversity. Despite their high diversity, tropical forests are fragile ecosystems and are less capable to recover from repeated human depredations than temperate forests. Tropical humid forests in general are amongst themost diverse, most productive andmost threatened of the biological communities with indeed 14 of the 18 biodiversity hotspots identified by Myers representing these biomes. Two of these hot spots viz., the Eastern Himalayas and the Western Ghats occur in India. But both these hot spots are threatened. To quote Dr. M. S. Swaminathan, both are paradises of valuable genes but are fast inching towards the status of “Paradise Lost.’’ At least 10 percent of India’s recorded wild flora and possibly more of its wild fauna are on the list of threatened species many of which are on the brink of obliteration. Of the wild fauna 80 species of mammals, 47 of birds 15 of reptiles, 3 of amphibians and a large number of moths, butterflies and beetles are listed as endangered. Out of 19 species of primates, 12 are endangered. The cheetah (Acinonyx jubatus) and the pink headed duck (Rhodonessa caryophyllacea) are among the well known conspicuous species that have become extinct; but there must be many more that have been totally annihilated unrecorded either because they were not that spectacular or because we simply were not aware of their existence (Balaji, 2010). Despite the discrepancy in the different estimates (Table 5.1) all prognoses lead to
the conclusion that what is taking place is not just loss of individuals but biodiversity as a whole is endangered.
